The present invention relates to a centrifuge, particularly a separator. The present invention also relates to a method for operation of the centrifuge.
Centrifuges and methods for their operation are known, for example, from German Patent Document DE 25 29 614 C2. That document describes a device for the continuous rotary pressure filtration of liquid media. Filtration, in the sense of that document are sieve as well as membrane filtrations as well as micro- or ultrafiltrations. By means of a hydrostatic pressure difference, a concentrate current component is generated parallel to the surface of the filter, for the purpose of which a hydrodynamic delivery pressure is generated in the ring gap between the centrifuge drum and the coaxial drum-shaped filter element in that the drum and the filter element are simultaneously acted upon by mutually different rotary frequencies. Without the independent relative rotatability, allegedly an extremely surface-laminar cross-current component would be created between the filters which has only so little effect that the fractionation process would already cease shortly after the start of the filtration as a result of polarization effects and pore sealing.
The separate rotatability of the sieve drum causes high constructive expenditures and therefore considerably increases the cost of the centrifuge.
It should also be noted that in the reference above, despite the relative rotatability of the sieve drum with respect to the centrifugal drum, a rerinsing of the membrane by means of a rinsing liquid is often required. However, such a rerinsing requires high expenditures and interrupts the centrifuging operation for a considerable period of time.
The present invention further develops the initially described centrifuge such that a constructively simple sieve or sieve system is provided in which solids can easily flow out of the sieve area and the pore sealing is reduced. In addition, a desirable method of cleaning the centrifuge obtained.
The present invention is a centrifuge, comprising a distributor for introducing material to be centrifuged and a sieve system having a plurality of axially mutually offset membrane plates. The membrane plates are arranged radially with respect to the distributor and have at least two axially-spaced membrane disks. The disks are connected with each other by at least one plate spacing ring in an area of the disks' outer circumference. The sieve system is arranged such that a flow direction of the material to be centrifuged emerging from the distributor and a flow direction of particles deposited on the membrane plates are identical. Also included is a centrifugal drum having a centrifugal compartment with the sieve system arranged therein. The centrifuge also includes a piston slide valve for closing the centrifugal drum.
Thus, the sieve system of the present invention is designed and arranged such that the flow direction of the material to be centrifuged emerging from the distributor and the flow direction of particles deposited on the sieve elements of the sieve system is identical. This results in a disturbance-free transport. A separate rotatability of the sieve system relative to the drum, as is known in the art, is also no longer required.
For example, the sieve system of the present invention comprises at least one—but preferably several—sieve plate(s) which is/are arranged essentially radially with respect to a distributor and may be designed as a membrane plate or plates made of a ceramic material. The distributor may also be a feed tube, or there may be a separate feed tube. As a result of the flow direction of the centrifuged or charged material between the membrane plates toward the outside, the flow direction of the solids deposited on the membrane, whose transport takes place toward the outside because of the centrifugal effect, is identical.
A piston slide valve for opening and closing the centrifugal drum is preferably provided. A solids-enriched stage is drained from a solids space of the centrifugal drum by way of openings—preferably nozzles—in the outside diameter of the solids space and/or by way of ducts/bores toward the centrifugal drum head or feed end. Concerning such a draining by means of nozzles at the piston slide valve, reference is made to German Patent Document DE 22 14 487.
For the cleaning as well as for the draining, the solids space centrifuge compartment is opened up—particularly by opening the piston slide valve—so that solids deposited and/or disposed on the sieve and/or impurities (and possibly also cloggings, deposited substances) are drained through the opening(s) opened up by the piston slide valve.
This cleaning can be carried out without any additional use of rinsing liquid and a rinsing by means of a rinsing liquid is required only after a relatively long operation.
It should be stressed that, because of modern control techniques, it is possible to very precisely control the evacuation mechanism and in this manner also control the cleaning effects in the desired fashion. As a result, a long service life of the sieve system or membrane insert is achieved without the requirement of a production stop because of clogging. Because of the speed of the evacuating mechanism and the permitted regulating of the discharge volume, the intensity of the cleaning effect can be controlled as a function of the product being centrifuged.
In another embodiment of the present invention, the draining of the concentrate is conceivable by way of a separating plate or small tube, ducts and nozzles outside the sieve system or membrane insert. As a function of the product being centrifuged, this may result in a lengthening of the rerinsing intervals (evacuation intervals). An automating of the point at which evacuation occurs is also possible by monitoring the stage being drained.
As another alternative, the carrying-away of a partial flow of the concentrate by way of nozzles is conceivable.
Instead of a piston slide valve, an analog operating, discontinuously working opening mechanism may be used.
The membrane plates may be mounted in the centrifugal drum individually as well as as a preassembled unit. This naturally offers advantages during the mounting/demounting.
In particular, the present invention combines in a simple manner the technology of modern piston slide valve separators known per se with the idea of a membrane plate insert and thereby creates a type of “membrane separator”.
The solids collection space preferably has a double-cone shape.
In particular, the invention provides a method of cleaning a centrifuge according to the present invention in the case of which, for cleaning the sieve system, preferably a piston slide valve of the centrifuge is opened up, so that a return flow of liquid through the sieve system removes substances deposited on or adhering to the sieve and/or impurities of the sieve.
Other aspects and novel features of the present invention will become apparent from the following detail description of the invention when considered in conjunction with the accompanying drawings.